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Re: 32 bit VS 64 bit modes

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Jason Damisch <jasondamisch@yahoo.com> writes:
> I thought that I'd ask... what the various trade-offs and advantages
> are between 32 bit and 64 bit modes.... it seems to me that 32 VS 64
> has diminishing returns.

Besides address space, 64 bits effectively gives more parallelism.  Like
if you're doing a memory block move without special instructions, doing
it 8 bytes at a time is much faster than with 4.  Similarly if you're
doing wide arithmetic.  

On the other hand, 64-bit programs consume more memory because pointers
are twice as wide, and (depending on language etc.) integers can be
twice as wide too.

> Maybe 40 bit would be ideal?

People want general purpose computers to have convenient byte addressing
these days, since they're often processing character data rather than
numerics.  So the word size is almost always a power of 2.  You see
sizes like 40 bits in specialized processors like DSPs where byte
addressing isn't as important.

> What reasons could there possibly be for having more than 4 GB of RAM?

"640k ought to be enough for anyone..." ;-).  More seriously, one
obvious benefit on PC's is that you can run lots of programs
simultaneously and still allot plenty of memory to each one.  As for
individual programs using GB's of ram, some programs like web browsers
do it, but that's an artifact of the ram being available and therefore
applications bloat up to use it.  Other programs like databases make
actual good use of the memory, though typically not on consumer
desktops.  

It's certainly true that bigger computers let you solve bigger problems.
I half-remember hearing OKAD could use up to a GB or so of ram when it
had the whole GA144 chip design in memory at once.  That's the most
memory intensive Forth program I can think of other than artificial
benchmarks, and of course it would use more with a bigger or more
complicated chip.  But in the benchmark category, Anton's program to
find the 10^9th Hamming number used an 8GB table, iirc.

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32 bit VS 64 bit modes Jason Damisch <jasondamisch@yahoo.com> - 2016-05-27 11:21 -0700
  Re: 32 bit VS 64 bit modes Paul Rubin <no.email@nospam.invalid> - 2016-05-27 13:06 -0700
    Re: 32 bit VS 64 bit modes Jason Damisch <jasondamisch@yahoo.com> - 2016-05-27 13:22 -0700
      Re: 32 bit VS 64 bit modes hughaguilar96@gmail.com - 2016-05-27 13:59 -0700
  Re: 32 bit VS 64 bit modes anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2016-05-28 10:07 +0000
    Re: 32 bit VS 64 bit modes Paul Rubin <no.email@nospam.invalid> - 2016-05-28 19:09 -0700
      Re: 32 bit VS 64 bit modes Paul Rubin <no.email@nospam.invalid> - 2016-05-28 20:00 -0700
      Re: 32 bit VS 64 bit modes Albert van der Horst <albert@cherry.spenarnc.xs4all.nl> - 2016-05-29 17:46 +0000
        Re: 32 bit VS 64 bit modes Paul Rubin <no.email@nospam.invalid> - 2016-05-29 11:27 -0700
  Re: 32 bit VS 64 bit modes Rod Pemberton <NoHaveNotOne@bcczxcfre.cmm> - 2016-05-28 23:42 -0400

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